Alberta a hot spot for liver parasite spread by canines, researcher says
A rare, potentially fatal parasitic disease from Europe found to be spread by canines has taken root in Alberta, now the North American hot spot for the infection.
A newly published review of known human alveolar echinococcosis (AE) cases found 17 in Alberta between 2013 and 2020, shows research led in part by University of Alberta infectious diseases expert Dr. Stan Houston.
Only two cases of human AE had been previously confirmed in North America — one in Manitoba in 1928 and another in Minnesota in 1977.
“This parasite has now become very widely established in the wild in the Prairies. It's been found in Saskatchewan and in B.C., but Alberta has had most of the cases of human disease,” said Houston in a Thursday news release from the U of A. “We have been having on average more cases every year. There's been a lull since COVID -19, but I'm suspicious it reflects a slowdown in testing during the pandemic and that we may soon see a surge again.”
The strain of AE found in the Alberta cases has been identified by scientists at the faculty of veterinary medicine in Calgary as having originally come from Europe, likely in dogs brought to the area.
The parasite takes the form of a tiny tapeworm in canines — typically foxes and coyotes, but potentially pet dogs — and is relatively harmless to them.
But when a rodent ingests parasite eggs from canine feces, it gets a different form of the disease and develops a deadly tumour, or parasitic growth, in the liver. And if the rodent is eaten by a canine, the parasite takes the tapeworm form again.
“We humans are taking the place of the rodent in the life cycle when we accidentally consume microscopic parasite eggs — maybe in strawberries or lettuce from a garden where a coyote passed through, or possibly a dog if it is carrying the parasite,” said Houston.
Likely contributing to the growth in Alberta cases is increasing human contact with urbanized coyotes and the number of people in the province who have weakened immune systems.
“In coyotes in Calgary and in Edmonton, more than half have been found to be carrying this parasite. So the new strain seems to not only be more virulent when it affects humans, but it seems to be super-effective in wild hosts,” said Houston.
“The COVID-19 pandemic has again elevated awareness of the number and importance of human diseases that are transmitted from animals.”
Of the 17 Alberta cases, 11 patients lived in rural areas, 14 owned dogs and six were immunocompromised individuals. The disease progresses faster in patients whose immune systems have been suppressed.
But the symptoms of AE can be elusive — several years may pass before a patient begins showing signs. Almost half of the cases in Alberta were found accidentally when the patient was getting tested for a different illness. Often it was found after an ultrasound showed abnormalities in the liver, followed by an investigative biopsy. When symptoms do occur, they can include unspecified pain, jaundice, weakness and weight loss — many of the same conditions expected from a cancerous liver tumour.
Because the parasite is initially symptomless, it is often able to slowly grow and by the time it is found, about two-thirds of patients will be inoperable. In those cases, lifelong anti-parasitic drugs are the only option. The most useful drug for controlling AE is not licensed in Canada and is only available through a special physician application process to both the government and manufacturer.
If left untreated, the parasite could kill its human host within 10 to 15 years.
Researchers are now working on a new study examining samples of liver biopsies from patients in Alberta where cancer wasn't found, to look for possible previously unrecognized cases of AE.
“That would give us a better picture of what's going on, but more importantly, would give us a chance to give those patients appropriate therapy,” said Houston.
“We should be paying attention, but it's still a very rare disease,” he added. “People should keep that in perspective, adopt healthy behaviours and not obsess about this.”
Avoiding the parasite comes down to good hygiene practices, like washing hands after handling a dog, especially if you suspect it's eaten a rodent or spent time in a dog park or area where coyotes frequent. Thoroughly washing produce that comes from the ground or close to the ground, such as lettuce or mushrooms, is also recommended.
The study, “Epidemiological and Clinical Characteristics of Alveolar Echinococcosis: An Emerging Infectious Disease in Alberta, Canada,” was published in The American Journal of Tropical Medicine and Hygiene.